In most municipal and industrial treatment facilities wastewater and sewage is purified in aerobic treatment processes. Bacteria and other microorganisms which occur naturally within sewage are cultured to consume organic wastes in aeration tanks. In these tanks the microbes multiply and digest the organic matter present in the wastewater. This process yields treated water, carbon dioxide, and a biomass of microbes which settles as a sludge in a clarifier connected to the aeration tanks. Some of the biomass is recycled to the tanks to reseed the system. The excess biomass, which is referred to as "waste activated sludge", is typically destroyed or otherwise disposed of. Costs associated with dewatering and disposing waste activated sludge can be substantial. Similar sludge management problems arise with other types of aerobic biological wastewater treatment systems, such as sequencing batch reactors and rotating biological contactors.
Various systems for conditioning sludge are known in the prior art. Some systems operate at elevated pressures or temperatures in order to increase bacterial digestion rates. For example, U.S. Pat. No. 4,192,741 issued Mar. 11, 1980 relates to a process for treating sewage effluent which includes the step of passing the activated sludge through a high pressure venturi to promote microbial activity.
It is also known in the prior art to condition activated sludge by pH adjustment. U.S. Pat. No. 3,718,582 issued Nov. 14, 1972 describes a microbial biolysis process in which the activated sludge is made alkaline by the addition of caustic soda and then hydrolyzed at an elevated temperature.
Maceration of sludge is commonplace as well. U.S. Pat. No. 3,658,262 which issued on Apr. 25, 1972 describes a grinder to reduce the size of sludge particles prior to thermal conditioning.
While such prior art systems are useful in reducing the volume of waste activated sludge, they typically result in increased energy, heating and/or materials costs. Accordingly, they do not meet the need to destroy or dispose of the waste activated sludge in an economical fashion.
The inventors have devised a cost-effective means of liquefying waste activated sludge or the like by lyzing microorganisms present in the sludge using a very high pressure homogenizer nozzle. Homogenizers are in common use in many industrial applications. Chemical, pharmaceutical, dairy, specialty food and biotechnological facilities all use homogenizers to emulsify, disperse, mix and process their products.
Homogenizers have recently been designed for high pressure operation. Such homogenizers employ high pressure pumps which force fluid through a valve or nozzle having a restricted flow area. As the fluid moves through the restriction, the velocity increases and the pressure decreases according to Bernoulli's law. Intense hydrodynamic changes occur in the fluid as high-pressure potential energy is converted to low-pressure kinetic energy.
In the biotechnology field, homogenizers have been used for cell disruption for many years. Passing a water slurry of microorganisms through a homogenizer disrupts the cell walls, allowing the contents to be released. In this way, the proteins and enzymes produced by the microorganisms can be harvested. However, heretofore homogenization technology has not been applied on an industrial scale to the problem of waste activated sludge management.
The need has therefore arisen for an industrial scale process for liquefying microorganisms present in sludge or other biosolids employing high-pressure homogenization technology.